The present invention relates to medical diagnostic instruments, and more particularly, to such instruments for detecting abnormal heart functions.
Patients occasionally develop heart disease, the prompt and timely discovery of which can be determinative of patients"" health and survival. Until the 19th century, medical caregivers had to press their ears against patients"" chests in order to hear heart sounds. When the stethoscope (xe2x80x9cspy of the chestxe2x80x9d in Greek) was introduced by Renxc3xa9 Laennec (1781-1826), it enabled medical caregivers to hear heart sounds with improved ease and clarity. xe2x80x9cIn search of the perfect stethoscope that hears all heart sounds, and explains them to you.xe2x80x9d (Laennec)
The ballistic recoiling of the heart produces a vibration when it moves its apex upward, rightward, and against the underside of the chest wall before the ejection of blood. This motion or vibration is typically inaudible and infrasonic, having a sound frequency of less than about 30 Hertz. There are other low frequency, low amplitude vibrations which normally occur during cardiac filling. There are also abnormal cardiac vibrations with sound frequencies as low as about 10 Hertz, but of high amplitude that occur when the heart fills abnormally. The period of cardiac filling is called diastole, and when these abnormal vibrations occur, they indicate diastolic dysfunction of the heart. These abnormal vibrations during diastole are called pathologic gallops. Some gallops are faint and difficult to hear, and some are infrasonic.
There are two types of pathologic gallops of primary clinical significance: An S4 type of gallop, which occurs during late diastole; and an S3 type of gallop, which occurs during early diastole. Many gallops are palpable and visible even when they are inaudible. This is because they are of high-energy amplitude despite their low frequencies. Detection of gallops is very important, and can lead to the diagnosis and treatment of such cardiac disorders as hypertrophic heart syndromes, valvular lesions, cardiomyopathies, and congenital heart problems.
A visual and palpable assessment of cardiac motion of a patient in the supine position may be made at the left chest wall near the left breast. This location is called the cardiac apical impulse, and for purposes of clarity is also herein referred to as the cardiac apical impulse point. The cardiac apical impulse point is a single area typically less than about 15 millimeters in diameter. The skin motion at this location is normally caused by the recoiling of the heart when it moves its ventricular apex upward, rightward, and against the underside of the chest wall. Presently, medical caregivers may examine the heart motions at the cardiac apical impulse point by placing their fingertips against the skin at this point to enable tactile detection of apical impulses having sufficient amplitude.
Over the past 60 years, sophisticated and elaborate laboratory apparatus have been developed to detect and record heart movements, and enable medical caregivers to analyze the data for indications of abnormal heart conditions. The apexcardiogram (xe2x80x9cACGxe2x80x9d), for example, which was in popular use until the early 1980""s, was capable of revealing low frequency heart motions by means of electromechanical sensors affixed to a patient""s chest. The ACG signals were recorded on a strip chart recorder for later analysis. An electrocardiogram (xe2x80x9cEKGxe2x80x9d) and a separate phonocardiogram were required to be performed contemporaneous with the ACG in order to provide correlation between the low frequency heart motions and the additional heart signals. The three charts were then correlated, as by technicians, for later analysis by caregivers. Although this method was very useful for detecting heart irregularities in suspected cases, the time delay incurred by a patient between seeing a physician for referral to an ACG laboratory, testing in the laboratory by technicians, correlation of strip chart results, and analysis and diagnosis by at least one physician, generally hindered prompt and effective treatment in time-critical cases. In addition, the large expense for this labor-intensive procedure may have precluded its use in many instances.
By the mid-1980""s, the ACG had been generally displaced by the echocardiogram. The echocardiogram uses ultrasonic waves to monitor heart function and provides more detail than the ACG. Unfortunately, the echocardiogram suffers from some of the same drawbacks as the ACG, including the requirement for special laboratory testing and associated expense. Like the ACG, the echocardiogram also fails to produce recognizable sounds indicative of the infrasonic heart motions, and therefore fails to disclose a method for their discovery.
Various other prior art systems are also directed toward monitoring human heart function. For example, U.S. Pat. No. 5,218,969 to Bredesen et al. (xe2x80x9cthe ""969 patentxe2x80x9d) depicts an electronically enhanced stethoscope for detecting heart sounds. However, the ""969 patent teaches filtering out sounds below 50 Hz (see FIG. 3F). Since human hearing is generally recognized to extend to at least as low as 30 Hz, the stethoscope of the ""969 patent is not capable of detecting heart vibrations of frequency below the range of human hearing, even if it may amplify low amplitude sounds which are above 50 Hz. Accordingly, the electronic stethoscope of the ""969 patent does not detect infrasonic cardiac apical impulses, and in fact is incapable of detecting any phenomena emitting a frequency below 50 Hz.
U.S. Pat. No. 5,178,151 to Sackner (xe2x80x9cthe ""151 patentxe2x80x9d) shows another system for detection of heart irregularities. The ""151 patent shows placement of a plurality of motion transducers about the thoracic region of a patient""s chest wall. Blood vessel volume, blood pressure waveforms, and other thoracic motions including respiratory and cardiac apical motions are measured as conglomerate signals that must be further analyzed to determine the presence of heart irregularities. Due in part to its bulk, complexity, cost, and requirement for further analysis, this system suffers from design constraints that generally preclude its inclusion in a general caregiver""s office. The apparatus of the ""151 patent further lacks provision for transmitting the acoustic heart waveform data typically relied on during a routine physical examination.
The basic acoustic stethoscope, whether electronically amplified, filtered or not, can only be used to hear what Rene Laennec heard with his original wooden device. Only a small percentage of the vibrations of the heart are actually detected by an acoustic stethoscope. These audible vibrations range between about 40 Hertz to 500 Hertz and about 0.002 to 0.5 dynes/cm2 (amplitude). The remaining vibrations are inaudible because of the typical thresholds of human hearing. Infrasonic vibrations of sufficient amplitude have heretofore only been detectable with bulky, complex, and costly apparatus requiring labor intensive analysis. Heart gallops rest near the division of audible and infrasonic vibrations. Heart gallops have been called the heart""s xe2x80x9ccries for help.xe2x80x9d Detection of these vibrations is important in diagnosing cardiac pathology and is why palpation of the cardiac apical impulse is an extremely important, yet often neglected, part of the cardiac exam.
All in all, the above-described prior art fails to recognize the utility of detecting infrasonic heart motions and producing audible outputs that are indicative of those motions. Such prior art also fails to put infrasonic heart motion data in context with traditional acoustic heart data. It is therefore an object of the present invention to overcome the above-described significant drawbacks and disadvantages of the prior art.
The present invention is directed to a cardiac impulse detector for use in routine cardiac examinations, which employs a sensor capable of detecting infrasonic cardiac apical impulses of a patient. The detector produces audible and optionally visual outputs indicative of those impulses for contemporaneous consideration by a medical caregiver when the sensor is placed in contact with the patient""s skin surface at the cardiac apical impulse point.
In an embodiment of the present invention, a sensing protrusion or button is placed in contact with the skin surface of the patient at the patient""s cardiac apical impulse point. The cardiac apical impulse point is located near the left breast. The sensing button is mounted to a piezoelectric sensor, and causes the sensor to respond to the infrasonic heart motions or impulses at the cardiac apical impulse point of the patient. A circuit is electronically connected to the piezoelectric sensor and generates audible and visual outputs indicative of the heart motions. The piezoelectric sensor is housed in one end of an hourglass shaped housing, which provides the caregiver with a convenient grip for holding the device against the cardiac apical impulse point.
This embodiment of the detector further employs a traditional acoustic diaphragm mounted at the opposite end of the housing relative to the piezoelectric sensor. The acoustic diaphragm can transmit acoustic heart sounds to an earpiece worn by the caregiver when the acoustic end of the sensor housing is placed in contact with the patient""s chest, and a selection manifold has been rotated 180 degrees in order to transmit the traditional acoustic sounds instead of the signals indicative of infrasonic heart motions. The sounds may be electronically amplified and/or filtered. This embodiment has the distinct advantage of placing the audible signal indicative of an infrasonic cardiac impulse in temporal context with the traditional acoustic cardiac sounds familiar to the caregiver.
In accordance with another aspect of the present invention, an apparatus is provided for detecting infrasonic cardiac apical impulses of a patient. The apparatus comprises a flexible substrate including (i) a skin-contacting surface located on one side of the substrate that is disposable in contact with a skin surface region of a patient defining an infrasonic cardiac apical impulse point, and is movable with the contacted skin surface region in response to a subaudible motion of the contacted skin at the infrasonic cardiac apical impulse point; and (ii) a reflective surface located on an opposite side of the substrate relative to the skin-contacting surface and movable with the skin-contacting surface in response to a subaudible motion of the contacted skin at the infrasonic cardiac apical impulse point. A light source, such as a laser, is spaced apart from and faces the reflective surface of the substrate. The light source transmits light onto the reflective surface, and the reflective surface reflects light transmitted thereon by the light source. An optical sensor is spaced apart from and faces the reflective surface. The optical sensor receives reflected light directed by the reflective surface and generates a first signal indicative of movement of the reflective and skin-contacting surfaces and corresponding to a subaudible motion of the contacted skin at the infrasonic cardiac apical impulse point. An electric circuit is coupled to the optical sensor for generating (i) an audible output and/or (ii) a visual output, in response to the first signal and indicative of an infrasonic cardiac apical impulse.
In accordance with another aspect, the present invention is directed to a method for detecting infrasonic cardiac apical impulses of a patient, comprising the following steps:
(i) providing a flexible substrate including a skin-contacting surface located on one side of the substrate and a reflective surface located on an opposite side of the flexible substrate relative to the skin-contacting surface;
(ii) positioning the skin-contacting surface of the flexible substrate in contact with a skin surface region of the patient defining an infrasonic cardiac apical impulse point on the patient""s chest;
(iii) allowing movement of the skin-contacting and reflective surfaces of the flexible substrate with movement of the skin surface region of the patient in response to a subaudible motion of the skin at the infrasonic cardiac apical impulse point;
(iv) transmitting light from a light source onto the reflective surface of the flexible substrate positioned on the skin surface region of the patient defining the infrasonic cardiac apical impulse point;
(v) reflecting transmitted light from the light source with the reflective surface of the flexible substrate positioned on the skin surface region of the patient defining the infrasonic cardiac apical impulse point;
(vi) receiving with an optical sensor reflected light directed by the reflective surface, and generating a first signal indicative of movement of the reflective and skin-contacting surfaces and corresponding to a subaudible motion of the skin at the infrasonic cardiac apical impulse point;
(vii) processing the first signal electronically; and
(viii) generating (i) an audible output and/or (ii) a visual output, indicative of an infrasonic cardiac apical impulse.
A primary advantage of the present invention is that it may provide an efficient way to screen patients for abnormal infrasonic vibrations or pathological gallops during routine physical examinations, a clearly desirable improvement over current procedure which requires elaborate set-up of bulky apparatus. Other objects and advantages of the present invention will become apparent in view of the following Detailed Description of the Preferred Embodiments and accompanying drawings.